Dialysis systems having air traps with internal structures to enhance air removal

ABSTRACT

A dialysis fluid cassette includes a rigid portion defining first and second valve chambers, the rigid portion further defining an air separation chamber in fluid communication with the first and second valve chambers, the air separation chamber including a baffle and structured such that when the cassette is placed in a dialysis instrument, (i) the baffle extends upwardly from a bottom of the air separation chamber and (ii) first and second openings to the air separation chamber, communicating fluidly and respectively with the first and second valve chambers, are located near the bottom of the air separation chamber, such that the dialysis fluid is forced up one side of the baffle and down the other side of the baffle when flowing through the air separation chamber.

BACKGROUND

The examples discussed below relate generally to medical fluid delivery.More particularly, the examples disclose systems, methods andapparatuses for dialysis such as hemodialysis (“HD”) automatedperitoneal dialysis (“APD”).

Due to various causes, a person's renal system can fail. Renal failureproduces several physiological derangements. It is no longer possible tobalance water and minerals or to excrete daily metabolic load. Toxic endproducts of nitrogen metabolism (urea, creatinine, uric acid, andothers) can accumulate in blood and tissue.

Kidney failure and reduced kidney function have been treated withdialysis. Dialysis removes waste, toxins and excess water from the bodythat normal functioning kidneys would otherwise remove. Dialysistreatment for replacement of kidney functions is critical to many peoplebecause the treatment is life saving.

One type of kidney failure therapy is Hemodialysis (“HD”), which ingeneral uses diffusion to remove waste products from a patient's blood.A diffusive gradient occurs across the semi-permeable dialyzer betweenthe blood and an electrolyte solution called dialysate to causediffusion. Hemofiltration (“HF”) is an alternative renal replacementtherapy that relies on a convective transport of toxins from patient'sblood. This therapy is accomplished by adding substitution orreplacement fluid to the extracorporeal circuit during treatment(typically ten to ninety liters of such fluid). That substitution fluidand the fluid accumulated by the patient in between treatments isultrafiltered over the course of the HF treatment, providing aconvective transport mechanism that is particularly beneficial inremoving middle and large molecules (in hemodialysis there is a smallamount of waste removed along with the fluid gained between dialysissessions, however, the solute drag from the removal of thatultrafiltrate is not enough to provide convective clearance).

Hemodiafiltration (“HDF”) is a treatment modality that combinesconvective and diffusive clearances. HDF uses dialysate flowing througha dialyzer, similar to standard hemodialysis, to provide diffusiveclearance. In addition, substitution solution is provided directly tothe extracorporeal circuit, providing convective clearance.

Most HD (HF, HDF) treatments occur in centers. A trend towards homehemodialysis (“HHD”) exists today in part because HHD can be performeddaily, offering therapeutic benefits over in-center hemodialysistreatments, which occur typically bi- or tri-weekly. Studies have shownthat a patient receiving more frequent treatments removes more toxinsand waste products than a patient receiving less frequent but perhapslonger treatments. A patient receiving more frequent treatments does notexperience as much of a down cycle as does an in-center patient who hasbuilt-up two or three days worth of toxins prior to a treatment. Incertain areas, the closest dialysis center can be many miles from thepatient's home causing door-to-door treatment time to consume a largeportion of the day. HHD can take place overnight or during the day whilethe patient relaxes, works or is otherwise productive.

Another type of kidney failure therapy is peritoneal dialysis, whichinfuses a dialysis solution, also called dialysate, into a patient'speritoneal cavity via a catheter. The dialysate contacts the peritonealmembrane of the peritoneal cavity. Waste, toxins and excess water passfrom the patient's bloodstream, through the peritoneal membrane and intothe dialysate due to diffusion and osmosis, i.e., an osmotic gradientoccurs across the membrane. Osmotic agent in dialysis provides theosmotic gradient. The spent dialysate is drained from the patient,removing waste, toxins and excess water from the patient. This cycle isrepeated.

There are various types of peritoneal dialysis therapies, includingcontinuous ambulatory peritoneal dialysis (“CAPD”), automated peritonealdialysis (“APD”), tidal flow dialysate and continuous flow peritonealdialysis (“CFPD”). CAPD is a manual dialysis treatment. Here, thepatient manually connects an implanted catheter to a drain to allowspent dialysate fluid to drain from the peritoneal cavity. The patientthen connects the catheter to a bag of fresh dialysate to infuse freshdialysate through the catheter and into the patient. The patientdisconnects the catheter from the fresh dialysate bag and allows thedialysate to dwell within the peritoneal cavity, wherein the transfer ofwaste, toxins and excess water takes place. After a dwell period, thepatient repeats the manual dialysis procedure, for example, four timesper day, each treatment lasting about an hour. Manual peritonealdialysis requires a significant amount of time and effort from thepatient, leaving ample room for improvement.

Automated peritoneal dialysis (“APD”) is similar to CAPD in that thedialysis treatment includes drain, fill and dwell cycles. APD machines,however, perform the cycles automatically, typically while the patientsleeps. APD machines free patients from having to manually perform thetreatment cycles and from having to transport supplies during the day.APD machines connect fluidly to an implanted catheter, to a source orbag of fresh dialysate and to a fluid drain. APD machines pump freshdialysate from a dialysate source, through the catheter and into thepatient's peritoneal cavity. APD machines also allow for the dialysateto dwell within the cavity and for the transfer of waste, toxins andexcess water to take place. The source can include multiple steriledialysate solution bags.

APD machines pump spent dialysate from the peritoneal cavity, though thecatheter, and to the drain. As with the manual process, several drain,fill and dwell cycles occur during dialysis. A “last fill” occurs at theend of APD and remains in the peritoneal cavity of the patient until thenext treatment.

In any of the above modalities, entrained air and other gases are aconcern. Entrained air can cause inaccuracies when pumping dialysate foreither PD or HD. Entrained air can cause a reduction in effectivesurface area in a hemodialysis filter when it accumulates on the filterfibers, leading to a reduction in the effectiveness of the therapy.Entrained air entering a patient's peritoneum during PD can causediscomfort. Entrained air entering a patient's bloodstream during HD canhave severe consequences. Accordingly, a need exists to provide anapparatus that ensures that entrained air is removed from dialysate orblood prior to delivering such fluids to the patient.

SUMMARY

The present disclosure relates to air and gas removal for dialysissystems and extracorporeal devices, e.g., blood separation, bloodwarming, etc. The structures disclosed herein can be performed in anytype of peritoneal dialysis treatment or blood dialysis treatment suchas hemodialysis, hemofiltration, hemodiafiltration and continuous renalreplacement therapy. The embodiments below are disclosed in connectionwith a dialysis cassette that is loaded into a dialysis instrument. Thedialysis cassette is part of an overall dialysis set which can includeone or more supply bag, or connection to the dialysate generationsystem, one or more drain bag, a heater bag and associated tubingconnecting the bags to the dialysis cassette. The user places thedialysis cassette within the dialysis instrument for therapy. Thedialysis cassette can include one or more pump chamber, flow path and/orvalve chamber. The dialysis instrument includes one or more pumpactuator that actuates the pump chamber of the disposable cassette. Thedialysis instrument also includes one or more valve actuator thatactuates the valve chamber of the disposable cassette. The disposablecassette can also include a fluid heating pathway that operates with afluid heater of the dialysis instrument. The disposable cassette canalso include various regions for sensing pressure, fluid composition,fluid temperature, and fluid levels.

While air traps 50 are shown herein in connection with a disposable setdescribed below, the separation chambers are alternatively stand-aloneapparatuses that operate independent of the disposable cassette.Further, the present disclosure mainly discusses air but other gases canalso be present and therefore the present air separation chambers canalso trap these gases. In PD for example, gases from the patient canbecome entrained in fluid being pumped form the system. Also, gases fromdialysate concentrate, such as bicarbonate can become entrained in freshdialysate. It is expressly contemplated for the air separation chambersof the present disclosure to remove these additional types of gases.

As mentioned above, air in dialysate or dialysis fluid as well as air inblood needs to be removed before any of these fluids are eitherdelivered to a dialyzer or patient. Air can be present in the system viaair trapped in supply bags, air trapped in the tubes leading from thesupply bags to the disposable cassette, air not completely primed fromthe disposable cassette itself and air that is released from solutionwhen the dialysis fluid is mixed and/or heated. Air can also signal aleak in the disposable unit.

The air traps discussed below are shown generally in connection with adialysis fluid, such as dialysate, having entrained air. It should beappreciated however that the embodiments are applicable equally to theremoval of air from blood pumped from a patient to a hemodialyzer orhemofilter. As used herein, the term dialysis fluid includes, withoutlimitation, mixed dialysate, mixed infusate, mixed replacement fluid,concentrated components of any of these, and blood.

In one embodiment, the disposable cassette defines an air separationchamber that has a fluid inlet and a fluid outlet. An inlet valve and anoutlet valve are paired with the fluid inlet and fluid outlet of the airseparation chamber, respectively. The air separation chamber alsoincludes an air vent outlet, which is in fluid communication with one ormore air vent valve. The air removed from fluid in the air trap is sentto atmosphere, to a holding vessel such as an empty bag or a fluidfilled bag (e.g, saline bag or dialysate bag), or to a drain, forexample, whichever is desired.

In one embodiment, the air separation chamber is configured with respectto the other components of the disposable cassette such that when thecassette is loaded into the dialysis instrument, the fluid inlet andfluid outlet are located towards a bottom or bottom wall of the airseparation chamber, while the air outlet is located at or near the topof the dialysis instrument. Such configuration allows buoyancy forces tolift air bubbles from the dialysis fluid to the top of the airseparation chamber for venting.

The dialysis cassette in one embodiment includes a rigid portion, whichcan be a hard plastic. The rigid portion is formed to have pump chambers(e.g., for diaphragm pumps) or pump tubing (for peristaltic pumping),fluid pathways and valve chambers. The rigid portion also defines someor all of the air separation chamber. It is contemplated that thedisposable cassette will have flexible sheeting welded to one or bothsides of the rigid portion of the cassette. The flexible sheeting allowsa pneumatic or mechanical force to be applied to the pump chambers(e.g., diaphragm) and valve chambers to operate those chambers. It isalso contemplated that at least one outer surface of the air separationchamber consumes a portion of one or both flexible sheets. In addition,one or both sides of the dialysis cassette can be rigid.

The disposable cassette can have a base wall or mid-plane that dividesthe disposable cassette into first and second sides. For example, in oneembodiment the flow paths are provided on one side of the disposablecassette (one side of the base wall), while the pump and valve chambersare provided on the other side of the disposable cassette. The airseparation chamber in one embodiment is provided on either the first orsecond side, whichever is more convenient. Here, the air separationchamber has one side surface that is a rigid mid-plane and a second sidesurface that is cassette sheeting. The cassette sheeting is welded to anair separation chamber inlet wall, an air separation chamber outletwall, an air separation chamber top wall and an air separation chamberbottom wall, which each extends from and is formed with the mid-plane ofthe rigid portion.

It is expressly contemplated however to make the outer wall of thedisposable cassette from a rigid material rather than from cassettesheeting. For example, a rigid piece could be welded, adhered orotherwise sealingly bonded to the air separation walls extending fromthe mid-plane of the rigid portion, or could be formed as one piecealong with the mid-plane of the rigid portion during manufacture.

In still a further alternative embodiment, the mid-plane is not presentwithin the air separation chamber, but the air separation chamber isbonded on two-sides by flexible sheeting. Still further alternatively,the mid-plane is not provided, however, the outer walls of the airseparation chamber are rigid and adhere to the top, bottom, inlet andoutlet walls via a suitable sealing process.

The air separation chamber includes one or more baffle or separationwall that is configured to disrupt the flow of fluid through the airseparation chamber, promoting the separation of air from the dialysisfluid. In one embodiment, the baffle or separation wall is a single wallformed of the rigid material and extending upward from a base wall ofthe air separation chamber. The single baffle wall can be parallel tothe inlet and outlet walls. Alternatively, the baffle is angled relativeto one or both the inlet and outlet air chamber walls. The inlet andoutlet air chamber walls can themselves be squared with the side wallsof the disposable cassette. Alternatively, the inlet and outlet airseparation chamber walls are angled with respect to the cassette sidewalls. For example, the air separation chamber can form a parallelogramshape with the inlet and outlet walls at a nonorthogonal angle withrespect to the top and bottom walls of the air separation chamber. Thebaffle can be angled the same as or different than the inlet and outletwalls.

In one embodiment, inlet and outlet pathways leading to and from the airseparation chamber inlet and outlet are inline with each other and aredisposed at least substantially perpendicular to an air vent pathwayleading out of the top of the disposable cassette. Here, the inlet andoutlet pathways can be at least substantially horizontally disposed whenthe disposable cassette is loaded into the dialysis instrument.Alternatively, the inlet and outlet pathways are not aligned with eachother and are provided at a non-horizontal angle. Indeed, in oneembodiment, the inlet and outlet pathways are at least substantiallyvertically disposed and parallel to the air vent pathway when thecassette is loaded for operation.

The baffle is not limited to being a single plate and can instead be apolygonal shape formed from one or more wall extending within the airseparation chamber. For example, the polygonal shape can have a wallthat includes a straight or nonlinear surface. The nonlinear surface canextend from the bottom wall of the air chamber upwardly towards the airvent, change direction towards the outlet of the air chamber and thenextend downwardly to the bottom wall of the air separation chamber. Thepolygonal baffle removes a volume within the air separation chamber suchthat the volume is separated from the dialysis fluid. The removed volumecan be a solid rigid material or can be a hollow volume beneath thebaffle wall.

The surface of the polygonal baffle forces the fluid to change directionat least once between the dialysis fluid inlet and the dialysis fluidoutlet of the air separation chamber. The polygonal shape of the bafflecan have one or more straight side so as to form a triangle or rectanglewithin the air separation chamber. The polygonal shape can be curved soas to form a semicircle within the air separation chamber. Furtheralternatively, the polygonal shape can have a combination of straightand curved surfaces.

While many of the embodiments below show the single wall or polygonalbaffle extending from the bottom wall of the air separation chamber, itis expressly contemplated to extend the baffle from a wall differentfrom the bottom wall. The baffle can instead be located above the bottomwall and extend for example from the mid-plane of the rigid portion.This baffle can also be a single wall baffle or a polygonal bafflehaving multiple walls or a single continuous wall. The baffle an beutilized as a barrier which forces the fluid to overflow or creates aconstriction between another structural feature such that the fluid isforced to flow through.

It is further contemplated to provide multiple baffles within the airseparation chamber. The multiple baffles can be any combination ofsingle wall, polygonal shape, attached to or not attached to the bottomwall, and perpendicular or angled with respect to the dialysate inletand outlet. A second baffle can for example extend from a surface of thefirst baffle. For example, a second single wall baffle can extend from afirst polygonal baffle. Further alternatively, multiple single wallbaffles can extend from the same polygonal baffle or from differentpolygonal baffles.

In still a further alternative embodiment, the baffle is configured tofloat within the air separation chamber. That is, the baffle is notconnected to any of the walls of the rigid portion of the disposablecassette and instead is moveable independently within the air separationchamber. For example, the air separation chamber can include a pluralityof spheres or other shaped members, which are too large to fit throughany of the dialysate inlet, dialysis fluid outlet or air chamberopenings. The plural spheres provide increased surface contact area withthe fluid to better remove air bubbles from the liquid. Additionally,the free motion accorded to the baffle (or plurality of baffles) allowstheir potion to disrupt air bubbles that may have accumulated throughsurface tension onto various surfaces within the chamber or onthemselves. This disruption allows the bubbles to be coalesced intolarger bubbles and carried to the air/fluid interface of the chamber forventing. Alternatively, a loose fitting geometry, such as a coiled ortwisted strip of plastic, is moveable within the air separation chamberto provide a large contact surface area with the dialysis fluid and toroute fluid towards the air/fluid interface of the chamber where bubblescan be separated from the fluid. To this end, the spheres or othershaped members can be textured to provide even additional surfacecontact area. In an alternate stationary geometry, the geometry can berigid on the air trap.

It is further contemplated to provide a nozzle at the air separationchamber inlet, which causes the inlet dialysis fluid to form a spray ormist, which further aids in removing air from the dialysis fluid. Stillfurther, it is contemplated to provide a vibrator, such as an ultrasonicor mechanical vibrator within the disposable cassette, which contacts aportion of the disposable set, such as a portion of the disposablecassette. The vibrator vibrates the disposable cassette to further aidin dislodging air bubbles from the dialysis stream and to aid in theircoalescence that increases the bubbles' buoyancy force, thereby inducingthem to float to the surface of the chamber for venting. In anembodiment, the ultrasonic or other type of vibrator is positionedwithin the dialysis instrument to contact the disposable cassette at theair separation chamber. The vibrator provides a force in addition tobuoyancy to separate air from the fluid, forming an air separation area.The air separation area attacks entrained air on multiple fronts, oneusing the above described baffles and another using the ultrasonic orother type of vibration. It is further contemplated to add the nozzle atthe inlet to this two-pronged air separation attack to form athree-pronged attack.

It is accordingly an advantage of the present disclosure to provideimproved air separation chambers for the removal of air from thedialysis fluid or blood flowing through a disposable dialysis fluidapparatus.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is one elevation view of one embodiment of a dialysis fluid airtrap of the present disclosure.

FIG. 2 is another elevation view of one embodiment of a dialysis fluidair trap of the present disclosure.

FIG. 3 is further elevation view of one embodiment of a dialysis fluidair trap of the present disclosure.

FIG. 4 is still another elevation view of one embodiment of a dialysisfluid air trap of the present disclosure.

FIG. 5 is still a further elevation view of one embodiment of a dialysisfluid air trap of the present disclosure.

FIG. 6 is yet another elevation view of one embodiment of a dialysisfluid air trap of the present disclosure.

FIG. 7 is yet a further elevation view of one embodiment of a dialysisfluid air trap of the present disclosure.

FIG. 8 is an eighth elevation view of one embodiment of a dialysis fluidair trap of the present disclosure.

FIG. 9 is a ninth elevation view of one embodiment of a dialysis fluidair trap of the present disclosure.

FIG. 10 is simulations of the dialysis fluid air trap of FIG. 9 inoperation.

FIG. 11 is a tenth elevation view of one embodiment of a dialysis fluidair trap of the present disclosure.

FIG. 12 is an eleventh elevation view of one embodiment of a dialysisfluid air trap of the present disclosure.

FIG. 13 is a twelfth elevation view of one embodiment of a dialysisfluid air trap of the present disclosure.

FIG. 14 is an elevation view of a dialysis instrument and cassetteoperable with the instrument, wherein the instrument includes a vibratorfor vibrating the disposable cassette to remove air from fluid flowingthrough the cassette.

DETAILED DESCRIPTION

Referring now to the drawings and in particular to FIG. 1, dialysiscassette 10 having air trap 50 illustrates one embodiment of the presentdisclosure. Dialysis cassette 10 is operable with any type of dialysisinstrument, such as a peritoneal dialysis instrument, hemodialysis,hemofiltration, hemodiafiltration or continuous renal replacementtherapy instrument. Dialysis cassette 10 can hold a dialysis fluid, suchas dialysate or blood. The dialysis fluid can be premixed or cassette 10can carry a component of dialysate such as a dialysate concentrate.

Dialysis cassette 10 in one embodiment is part of a disposable set,which includes one or more supply bag, a drain bag, a heater bag, andtubing running from those bags (not illustrated) to dialysis cassette10. Dialysis cassette 10 in one embodiment is disposable, however,dialysis cassette 10 could be cleaned for multiple uses in which casethe air traps described herein are used multiple times. Dialysiscassette 10 includes a rigid portion have a cassette top wall 12, acassette side wall 14 and a cassette bottom wall 16. Suitable materialsfor the rigid portion include polyvinyl chloride (“PVC”), acrylic, ABS,polycarbonate, and polyolefin blends. The rigid portion of cassette 10also includes a base wall or mid-plane 18, which separates cassette 10into first and second sides.

The side of mid-plane 18 illustrated in FIG. 1 includes pump chambers 20a and 20 b, which here are part of a pneumatically and/orelectromechanically operated diaphragm pump. Alternatively, cassette 10includes peristaltic pumping tubes that operate with a peristaltic pumpactuator of the dialysis instrument. Cassette 10 also includes valvechambers, such as air separation chamber inlet valve chamber 22, airseparation chamber outlet valve chamber 24 and air separation chamberair vent valve chambers 26 a and 26 b. The valve chambers can also bepneumatically and/or electromechanically operated.

The other side of cassette 10, which is divided by mid-plane 18 (notillustrated), can include flow paths and/or other valve chambers and/orpump chambers. It should be appreciated that cassette 10 can havedifferent structural layouts without affecting the performance airseparation chamber 50. Air separation chamber 50 can be located oneither side of mid-plane 18 for space purposes or for other reasonsrelated to component layout.

In the illustrated embodiment, the rigid portion of cassette 10 definesthe wall or walls of pump chambers 20 a and 20 b, which in theillustrated embodiment operate with a flexible cassette sheeting 28,which is welded, heat sealed or solvent bonded to rigid walls 12, 14,16, etc., of the rigid portion of cassette 10. Suitable cassettesheeting 28 includes polyvinyl chloride (“PVC”),polypropylene/polyethylene blends, polypropylene or Kraton blends,polyester, polyolefin, and ULDPE. The suitable PVC sheeting can include,for example, monolayer PVC films, non-DEHP PVC monolayer films,monolayer non-PVC and multilayer non-PVC films (wherein different layersare chosen to provide strength, weldability, abrasion resistance andminimal “sticktion” to other materials such as rigid cassettematerials). Multiple layers can be coextruded or laminated with orwithout a gas barrier.

Cassette sheeting 28 is also used to open and close valve chambers, suchas chambers 22, 24, 26 a and 26 b. The dialysis instrument includes acontroller unit that operates a program that controls when valves 22,24, 26 a and 26 b are opened or closed. The controller unit can include,but is not limited to, a processor, memory, hardware (e.g. sensors,actuators, I/O boards, etc.), software, and algorithms. For example,inlet and outlet valves 22 and 24 can be sequenced during priming tofill the air separation chamber. Inlet and outlet valves 22 and 24 areopen during dialysis fluid delivery and/or blood pumping to remove airfrom those fluids. While inlet and outlet valves 22 and 24 are showndirectly in front of and behind the air separation chambers, it is alsocontemplated to move one or both the inlet and outlet valves 22 and 24further away from the air separation chamber. One or both of inlet andoutlet valves 22 and 24 can be configured to control flow to multipleplaces within cassette 10, including the air separation chamber.

The controller unit is also programmed to operate vent valves 26 a and26 b so as to remove air from the air separation chamber in a manner soas not to effect the sterility of the dialysis fluid flowing throughcassette 10. To this end, the controller unit can operate with a signalfrom an optical or ultrasonic sensor monitoring the level of fluidwithin the air separation chamber. Alternatively, the controller unitcan operate with an air pressure signal from a pressure sensormonitoring the pressure of air in the chamber. In either case, thesignal is monitored to determine when to perform the air purge valvesequence of valves 26 a and 26 b. Alternatively, the controller unit isprogrammed to perform the valve sequence for valves 26 a and 26 b at setintervals.

Cassette 10 in FIG. 1 also includes a plurality of rigid ports extendingfrom one of the walls, such as cassette top wall 12. In the illustratedembodiment, cassette 10 includes a vent port 30, which operates withvent valves 26 a and 26 b and air separation chamber 50. Cassette 10also includes other ports, such as one or more fluid supply port 32, adrain port 34, a to- or from- heater port 36 and other ports, such as apatient port and a heater bag port.

Vent port 30 can vent air from air separation chamber 50 to atmosphereor to drain in different embodiments. Cassette 10 can include otherapparatuses (not illustrated), such as pressure sensing areas, heaterflow path areas, and additional pumping areas, such as heparin and/orsaline pumping areas.

Air trap 50 refers generally to each of the air traps 50 a to 501discussed herein. FIG. 1 shows one embodiment of the air separationchamber or air trap of the present disclosure, namely, air separationchamber 50 a. Air separation chamber 50 a includes an inlet wall 52, abottom wall 54, an outlet wall 56 and a top wall 58. Walls 52 to 58 canextend from mid-plane 18, such that mid-plane 18 forms one of the broadsides of air separation chamber 50. Alternatively, mid-plane 18 extendsalong the outside of walls 52 to 58 but not inside air separation 50,such that walls 52 to 58 extend the entire thickness of cassette 10.Here, both broad surfaces of air separation chamber 50 can be made offlexible sheeting 28.

Alternatively, one or both of the broad surfaces of air separationchamber 50 are made of the rigid material, wherein sheeting 28 is weldedto the broad surfaces of air separation chamber 50. For example, theprofile shape of air separation chamber 50 can be welded or solventbonded to walls 52 to 58. Thereafter, the sheeting is welded or solventbonded to the edges of the rigid broad sides of air separation chamber50.

In the case where mid-plane 18 forms one of the broad sides of airseparation chamber 50, the outer broad surface of air separation 50 canbe flexible sheet 28 or a rigid piece, welded or solvent bonded to walls52 to 58.

Inlet valve 22 opens or closes an inlet pathway 62, while outlet valve24 opens or closes an outlet pathway 64. Inlet pathway 62 communicateswith air separation chamber 50 via inlet 66, which is formed in wall 52of air chamber 50. Outlet pathway 64 communicates with air separationchamber 50 via an outlet 68 formed in wall 56 of air separation chamber50. It should be appreciated that while valves 22 and 24 are shown asinlet and outlet valves, respectively, each valve can be either an inletor an outlet valve, e.g., for priming purposes both valves 22 and 24 maybe inlet valves that prime fill chamber 50 a up to a predetermined fluidlevel within the chamber.

Vent valves 26 a and 26 b open and close a vent line 70. Vent 70communicates with vent port 30 and with air separation chamber 50 via avent outlet 72 formed in top wall 58 of air separation chamber 50. Dualvent valves 26 a and 26 b allow the controller unit of the dialysisinstrument to isolate a slug of air in vent line 70 before vent valve 26b is opened, allowing the air to escape via vent port 30 to atmosphereor drain. In the programmed sequence, with vent valve 26 b closed, ventvalve 26 a is opened allowing vent line 70 to become pressurized withair. Once line 70 becomes pressurized, valve 26 a is closed and valve 26b is opened, relieving the pressure in vent line 70.

With air separation chamber 50 a, inlet pathway 62 and outlet pathway 64are aligned with each other and are at least substantially perpendicularto vent line 70. Walls 52 and 56 are at least substantially orthogonalto walls 54 and 58, forming a square or rectangular air separationchamber 50.

Air separation chamber 50 a includes a single baffle 80 a, which asillustrated is a single wall extending vertically upwardly from bottomwall 54 past inlet 62 and outlet 64. Single baffle 80 a is also integralwith mid-plane 18 in one embodiment. Baffle 80 a forces the flow ofdialysis fluid 82 vertically upward from inlet 62 against the directionof gravity g, along a first surface of baffle wall 80 a. Baffle 80 a andoutlet wall 56 then force dialysis fluid 82 down a return surface ofbaffle wall 80 a, to outlet flow path 64 and to outlet valve 24. As theflow of dialysis fluid 82 rises and flows over separation wall or baffle80 a, the fluid it is slowed down due to increased cross-sectional areaof air chamber 50 a. Air is collected in the upper section 84 of chamber50 a. The primary purging action of air chamber 50 a is the force ofbuoyancy.

Referring now to FIG. 2, air separation chamber 50 b operable withcassette 10 includes many of the same features as air separation chamber50 a. Here however, inlet wall 52 and outlet wall 56 are taperedoutwardly from bottom wall 54 to top wall 58, producing an airseparation chamber having a substantially trapezoidal shape. The shapeof air separation chamber 50 b causes the dialysis fluid 82 flowcross-section to increase gradually in a vertical direction, enablingfurther slowing of the fluid, and allowing more time for buoyancy forcesto lift air bubbles from the dialysis fluid 82.

Single wall baffle 80 b in air separation chamber 50 b is tilted awayfrom the 90° vertical position of baffle 80 a, towards outlet line 64and outlet valve 24. Tilted baffle 80 b causes the cross-section ofdialysis fluid flow 82 on the inlet side of chamber 50 b to increaseeven more as dialysis fluid 82 flows vertically upward until reachingthe free end of baffle 80 b, further slowing the fluid and allowing moretime for buoyancy forces to lift air bubbles from the dialysis fluid 82.

Single wall baffles 80 a and 80 b and indeed any of the single wallbaffles describe herein (baffles 80) extend in one embodiment the totalthickness of the air separation chamber, for example, all the way frommid-plane 18 to the cassette sheeting 28. Alternatively, wall or baffle80 does not extend all the way across the width of the air separationchamber. In such case, additional gusseting or support can be provided.Also, additional support or gusseting can be provided to baffles 80 whenthe air separation chamber is bounded on both broad sides by flexiblesheeting 28.

FIG. 3 illustrates a further alternative air separation chamber 50 coperable with cassette 10, in which inlet wall 52 and outlet wall 56 arepositioned at a non-orthogonal angle with respect to bottom wall 54 andtop wall 58. The shape of air trap 50 c is substantially that of aparallelogram. Baffle 80 c is at least substantially the same as baffle80 b and is at least substantially aligned with the angled walls 52 and56 in air separation chamber 50 c. Besides increasing cross-sectionalflow area on the inlet side of baffles 80 b and 80 c, angling baffles 80b and 80 c in the direction shown also extends or lengthens the dialysisfluid 82 flow path along the left or inlet portion of the air separationchamber 50 a.

Air separation chamber 50 d of FIG. 4 operable with cassette 10illustrates that inlet path 62 and outlet path 64 are not aligned andare not orthogonal to vent line 70. The shape of air trap 50 d is onceagain polygonal. Angled baffle 80 d is the same as or similar to baffles80 b and 80 c. However, as illustrated in FIG. 4, the direction of theinlet and outlet pathways, 62 and 64 respectively, can be in directionsother than horizontal or vertical. Air separation chamber 50 d allows across-sectional area on the inlet portion of the valve chamber toincrease, such that fluid velocity slows as it fills over baffle 80 d.Outlet flowpath 64 angled as shown tends to lengthen the exit flow path,between baffle 80 d and outlet wall 56, of chamber 50 d since in thisconfiguration buoyancy and drag forces acting on the air bubbles are notin opposite directions. The buoyancy force is always opposite to thedirection of gravity whereas the drag force is opposite the velocity ofa particle. The bubbles would rise up and they will only feel a smallercomponent of the drag force opposing their rise.

Air separation chamber 50 e of FIG. 5 operable with cassette 10illustrates a number of additional concepts. Here, inlet and outletpathways 62 and 64 are vertical when cassette 10 is placed in anoperable position. Dialysis fluid flow 82 in pathways 62 and 64 isaccordingly aided or impeded by the force of gravity g.

Air separation chamber 50 e also has multiple baffles 80 e 2 and 80 e 3.Bottom wall 54 includes or has multiple surfaces or walls which forcedialysis fluid 82 upwardly through inlet pathway 62, over a curved ornonlinear portion of bottom wall 54, down a vertical wall of bottom wall54, and out outlet pathway 64. Air separation chamber 50 e includesfirst and second flow restrictions or baffles 80 e 2 and 80 e 3. Baffle80 e 2 is not connected to bottom wall 54 and instead extends frommid-plane 18. Baffle 80 e 2 forms a narrow channel 86 between the baffleand the top surface of bottom wall 54. Dialysis fluid flow 82 is forcedthrough channel 86. Second baffle 80 e 3 extends from bottom wall 54 andthus forces fluid to flow up over bottom wall 54.

The net effect of the two baffles 80 e 2 and 80 e 3 of air separationchamber 50 e is the creation, essentially, of three fluid regions 82 a,82 b and 82 c of dialysis fluid 82 within the air separation chamber.Each region resides above the curved surface of bottom wall 54. In theregions, dialysis fluid 82 flows into chamber 50 e through inlet pathway62 and into left chamber 82 a. Baffle 80 e 2 forces fluid to flowthrough a constriction 86 into middle region 82 b. Fluid velocity inregion 82 a decreases due to the restriction through opening to 84,aiding de-gassing due to buoyancy force. Fluid pressure builds in region82 a and a difference in fluid level as illustrated results betweenregions 82 a and 82 b.

Dialysis fluid 82 rises for a second time in large region 82 b,resulting in a slowed flow and a second opportunity to de-gas viabuoyancy forces. When the dialysis fluid level rises in region 82 b tothe free end of second baffle 80 e 3, the dialysis fluid 82 flows overbaffle 80 e 3 and begins to fill third region 82 c. The surface ofbaffle 80 e 1 is channeled slightly to allow the dialysis fluid 82 topool in both regions 82 b and 82 c while filling. Dialysis fluid 82rises to the edge of outlet pathway 64 and then flows out pathway 64,leaving air separation chamber 50 e. Depending on the dialysis fluid 82flowrate into region 82 c, the fluid level in the region may be the sameas (as shown) or lower than that of 82 b. Region 82 c aids in de-gassingany air bubbles remaining in dialysis fluid 82.

Air separation chamber 50 f of FIG. 6 operable with cassette 10 is verysimilar to air separation chamber 50 e of FIG. 5. Here however, secondbaffle plate 80 e 3 is not provided and instead curved wall 54 includesa hump at its exit side to decrease dead zones in the fluid flow inregion 82 b (i.e., areas of low or no fluid flow or stagnation). Also,baffle 80 f 2 is modified to have a triangular shape, further decreasingthe dead zones and increasing circulation zones. Angled exit 82 cincreases the amount of air bubbles that ride upwardly along theoutlet-side surface of baffle 80 f 2 because the drag force along thebaffle 80 f 2 and the buoyancy force are not co-linear. Outlet flowpath64 angled as shown tends to lengthen the exit flow path, between baffle80 f 2 and outlet wall 56, of chamber 50 e since in this configurationbuoyancy and drag forces acting on the air bubbles are not in oppositedirections. The buoyancy force is always opposite to the direction ofgravity whereas the drag force is opposite the velocity of a particle.The bubbles would rise up and they will only feel a smaller component ofthe drag force opposing their rise.

Air separation chamber 50 g of FIG. 7 operable with cassette 10illustrates a further modification of the air separation chamber 50 e ofFIG. 5. Here, three polygonal baffles 80 g 1 to 80 g 3 are eachpolygonal shape and positioned to create free flow regions. Again, theangled surfaces of polygonal baffles 80 g 1, 80 g 2 and 80 g 3 increasethe ability of those surfaces to carry bubbles upward due to a dragforce and buoyancy force differential. In this configuration, buoyancyand drag forces acting on the air bubbles are not in oppositedirections. The buoyancy force is always opposite to the direction ofgravity whereas the drag force is opposite the velocity of a particle.The bubbles would rise up and they will only feel a smaller component ofthe drag force opposing their rise. FIG. 7 further illustrates that oncediameter D1 and length L are determined, the dimensions of each of thebaffles 80 g 1, 80 g 2 and 80 g 3 as well as inlet wall 52, outlet wall56, bottom wall 54 and top wall 58 are also set. Fluid in regions 82 aand 82 b can fill to the dimensions shown, with the fluid in region 82 afilling to a slightly higher level.

The flow pattern of air separation chamber 50 g is similar to that ofchambers 50 e and 50 f. In a similar manner, dialysis fluid 82 is forcedfrom region 82 a to region 82 b through opening 86, allowing thedialysis fluid 82 to fill and de-gas for a second time in region 82 b.Dialysis fluid 82 eventually rises to the free end of polygonal baffle80 g 3 and flows over baffle 80 g 3 to outlet pathway 64. Depending onthe dialysis fluid flowrate into region 82 c, the fluid level in theregion may be the same as (as shown) or lower than that of 82 b. Region82 c aids in de-gassing any air bubbles remaining in the dialysis fluid82.

Air separation chamber 50 h of FIG. 8 operable with cassette 10 shows afurther modification over these air separation chambers of FIGS. 5 to 7.Here, outlet wall 56 is also angled to help air bubbles travel upwardstowards air collection portion 84 via third flow region 82 c. Similar toair separation chamber 50 g, air separation chamber 50 h includes threepolygonal baffles 80 h 1 to 80 h 3, which are each positioned to createfree flow regions.

Referring now to FIG. 9, air separation chamber 50 i operable withcassette 10 illustrates one preferred air separation chamber of thepresent disclosure. While chambers 50 e to 50 h of FIGS. 5 to 8 are veryeffective at removing air from dialysis fluid 82, chambers 50 e to 50 hconsume a fair amount of space within cassette 10. It is desirable froma manufacturability and cost standpoint to make cassette 10 smallerrather than larger. It has been found that the first portion of airseparation chambers 50 g and 50 h alone provides a very effective airremoval chamber. Thus it is believed that air separation chamber 50 iprovides a smaller but effective chamber. Similar structures to airseparation chamber 50 i are included in first regions 82 a of chambers50 g and 50 h and are also very effective in removing gas bubbles fromthe fluid as discussed above.

Air separation chamber 50 i as seen includes polygonal baffle 80 i,which has a triangular shape, including angled inlet surface 90 andangled outlet surface 92. Surfaces 90 and 92 can be straight (as shown)or curved. Angled inlet surface 90 forms a first dialysis fluid region82 a with inlet wall 52. The angled wall provides an increase in thecross-sectional flow area that slows the dialysis fluid 82 as it riseswithin region 82 a.

Angled outlet surface 92 forms a second dialysis fluid region 82 b withoutlet wall 56. As fluid fills past the apex of baffle 80 i, thecross-sectional area approximately doubles, further slowing the flow ofdialysis fluid 82 and allowing buoyancy forces to push air bubble fromthe fluid. Fluid exit 64 extends the outlet flow path similar to airseparation chamber 52 d such that the flow path is extended as much aspossible in the air trap. Fluid pathway 64 acts as a constricted exithaving a smaller cross-sectional area as compared with fluid inlet 62.Air collects in region 84 and is purged through air purge line 70.

As seen additionally in FIGS. 7 and 8, in one implementation if inletwall 52 and top wall 58 are each 2 L in length, sides 90 and 92 have avertical component of length L. The apex of baffle 80 i or theintersection of sides 90 and 92 occurs approximately at a distance Lfrom inlet wall 52 and outlet wall 56. This implementation as seen belowstrikes an effective balance by separating chamber 50 i into differentregions while allowing an ample common area for dialysis fluid 82 torelease air bubbles at the interface with air collection portion 84.

FIG. 10 illustrates an output of a simulation of air separation chamber50 i, showing pathways taken by larger air bubbles, approximatelyfive-hundred microns in diameter, trapped within dialysis fluid 82 whenflowing through air separation chamber 50 i at a certain flowrate and acertain fluid level.

Referring now to FIG. 11, air separation chamber 50 j operable withcassette 10 illustrates an additional concept of providing a nozzle 74at inlet 62. Nozzle 74 creates a mist or spray of fluid leaving thenozzle due to the low pressure at the exit of the nozzle. The formationof the spray causes de-gassing of the dialysis fluid 82 due to theincreased dialysis surface area that the mist creates, and in particularin combination with a negative pressure that may be present in chamber50 j, which would help to pull air from the fluid. One embodiment forproviding a nozzled flow into an air separation chamber is described inco-pending application entitled “Dialysis System Having Non-InvasiveFluid Velocity Sensors”, Ser. No. 11/876,619, filed Oct. 22, 2007, thepertinent portions of which are incorporated here expressly byreference. Nozzle 74 sprays inlet dialysis fluid 82 against a splashwall 76. Splash wall 76 causes air to de-gas from the dialysis fluid 82due to impact and also protects against fluid spray exiting through airline 70.

Dialysis fluid 82 falling down along splash plate 76 pools in a firstliquid region 82 a. A baffle 80 j forces the pooled fluid from region 82a through opening 86 caused by baffle 80 j into a second liquid region82 b. Fluid region 82 b provides another opportunity for liquid tode-gas due to buoyancy forces before the dialysis fluid 82 leaves exitfluid pathway 64.

Nozzle 74 may cause the exiting fluid to foam, which would not bedesirable for de-gassing blood in an HD blood circuit for example.However, air separation chamber 50 j is suitable for any dialysatecircuit.

Referring now to FIGS. 12 and 13, air separation chambers 50 k and 50 l,each operable with dialysis fluid cassette 10 illustrate furtheralternative embodiments of the present disclosure. Air separationchamber 50 k of FIG. 12 includes textured spheres or members 94, whichare placed loosely within air separation chamber 50 k. That is, spheresor members 94 are free to move within chamber 50 k. The particles aresized so as not to be able to fit into, or block flow through, any ofinlet line 62, outlet line 64 or air line 70. Suitable spheres can beobtained from McMaster-Carr, model number 9587K13, 1383K44, or similar.Spheres or members 94 introduce additional surface area for bubbles toattach to and be pulled from dialysis fluid 82. Spheres 94 also serve toagitate fluid flow through chamber 50 k, which has the dual benefit ofprecipitating air that may be dissolved in the fluid and dislodgingand/or coalescing bubbles that may have accumulated on the interiorchamber surface or sphere surface. The bubbles move upwardly andeventually de-gas into air portion 84. Spheres or members 94 alsoagitate the flow of liquid within air separation chamber 50 k, whichalso helps to free air bubbles from the dialysis fluid 82.

Air separation chamber 50 l of FIG. 13 illustrates a helical or coiledramp 96, which can be textured to produce additional surface area. Ramp96 in one embodiment is free to move within chamber 50 l. Ramp 96 can bemade of a suitable medical grade plastic, such as any of the materiallisted above for the rigid portion of cassette 10. Ramp 96 pulls bubblesout of the dialysis fluid 82 and also serves to turbulate or agitatefluid flow through chamber 50 l.

Referring now to FIG. 14, dialysis machine 100 illustrates a furtheralternative air separation apparatus and technique of the presentdisclosure. Dialysis machine 100 includes a main or instrument portion102 and a door 104, which opens and closes with respect to main portion102 to accept cassette 10. Cassette 10 can have any of the airseparation chambers 50 discussed above. In an embodiment, the airseparation chamber in operation is pressed against a contact transduceror vibrator 106, which is configured to vibrate the liquid 82 at the airseparation chamber. One suitable contract transducer 106 is provided byXactec Corporation, model number CM-HP-1/2-1.00. While one preferredembodiment is to vibrate the liquid at the air separation chamber 50, itshould be appreciated that contract transducer 106 can be configured toshake the entire cassette 10 or other portions of the cassette, such asa pump chamber to relieve air bubbles from the dialysis fluid 82.

It is accordingly contemplated to provide a multi-prong attack forremoving and trapping air from dialysis liquid. Each of: (i) inducingvibrations into the air separation chamber; (ii) providing the bafflesfor buoyancy removal; and/or (iii) providing the nozzle (with any of theair separation chambers 50 described herein) to mist the dialysis fluid82 into a spray and to increase fluid surface area, ultimately enablesthe gas to more readily pull from the fluid via negative pressure inorder to remove gas from the liquid.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A dialysis fluid cassette comprising: a rigid portion defining firstand second valve chambers; and the rigid portion further defining an airseparation chamber in fluid communication with the first and secondvalve chambers, the air separation chamber including a baffle andstructured such that when in an operating position, (i) the baffleextends upwardly from a bottom of the air separation chamber and (ii)first and second openings to the air separation chamber, communicatingfluidly and respectively with the first and second valve chambers, arelocated near the bottom of the air separation chamber, such thatdialysis fluid is forced up one side of the baffle and down another sideof the baffle when flowing through the air separation chamber.
 2. Thedialysis fluid cassette of claim 1, wherein the air separation chamberhas a shape selected from the group consisting of: at leastsubstantially rectangular, at least substantially trapezoidal and atleast substantially parallelogram.
 3. The dialysis fluid cassette ofclaim 1, wherein at least one surface of the air separation chamberincludes sheeting.
 4. The dialysis fluid cassette of claim 1, thecassette including a mid-plane, a surface of the air separation chamberbeing the mid-plane.
 5. The dialysis fluid cassette of claim 1, thebaffle (i) at least substantially perpendicular to the bottom of the airseparation chamber; or (ii) angled with respect to the bottom of the airseparation chamber.
 6. The dialysis fluid cassette of claim 1, the airseparation chamber having a third opening at a top of the chamber forventing air released from the dialysis fluid.
 7. The dialysis fluidcassette of the claim 6, the cassette including at least one air ventvalve chamber in fluid communication with the third opening.
 8. Thedialysis fluid cassette of claim 1, the cassette including first andsecond flow paths in fluid communication with the first and secondopenings, the first and second flow paths at least one of: (i) parallelwith respect to each other; (ii) angled with respect to each other;(iii) aligned; (iv) extending at least substantially perpendicular tothe baffle; and (v) extending at least substantially parallel to thebaffle.
 9. The dialysis fluid cassettes of claim 1, wherein the baffleis a single wall.
 10. The dialysis fluid cassette of claim 1, whereinthe baffle includes a polygonal shape.
 11. The dialysis fluid cassetteof claim 1, wherein the baffle includes at least two intersecting walls.12. The dialysis fluid cassette of claim 11, wherein at least one of thewalls is curved.
 13. The dialysis fluid cassette of claim 1, wherein thebaffle is a first baffle, and wherein the air separation chamberincludes a second baffle.
 14. The dialysis fluid cassette of claim 13,wherein at least one of the first and second baffle: (i) is a singlewall and (ii) includes a polygonal shape.
 15. The dialysis fluidcassette of claim 13, wherein at least one of the first and secondbaffle is at least one of: (i) attached to a bottom wall of the airseparation chamber; (ii) is not attached to the bottom of the airseparation chamber; (iii) extends from a surface of the other of thefirst and second baffle; (iv) extends from a side wall of the airseparation chamber; and (v) creates a fluid constriction within the airseparation chamber.
 16. A dialysis fluid air separation chambercomprising: a plurality of chamber walls; and a surface within the wallsforming a polygonal shape that forces dialysis fluid to flow above thepolygonal shape, the polygonal shape including a plurality of facesforming at least one angle between the faces.
 17. The dialysis fluid airseparation chamber of claim 16, the surface further including at leastone of: (i) the surface of the air separation chamber is non-linear;(ii) the surface when the air separation chamber is in an operatingposition extending above at least one fluid opening to the airseparation chamber; (iii) the surface forming a first baffle, and whichincludes a second baffle extending from the surface; (iv) the surfacebeing a first surface, and which includes a second surface forming asecond polygonal shape; and (v) a flat wall extends from the surface.18. A dialysis fluid cassette comprising: a rigid portion defining firstand second valve chambers; and the rigid portion further defining an airseparation chamber located between the first and second valve chambers,the air separation chamber when in an operating position including afirst baffle portion extending up from and angling inwardly from aninlet of the air separation chamber and a second baffle portionextending down from the first baffle portion and angling outwardlytowards an outlet of the air separation chamber.
 19. The dialysis fluidcassette of claim 18, wherein the first and second baffle portions areat least substantially straight, forming a triangular shape.
 20. Thedialysis fluid cassette of claim 18, the first baffle portion of the airseparation chamber ending and the second baffle portion beginningapproximately half-way across a horizontal width of the air separationchamber.
 21. The dialysis fluid cassette of claim 18, the first baffleportion ending and the second baffle portion beginning approximatelyhalf-way up a vertical height of the air separation chamber.
 22. Thedialysis fluid cassette of claim 18, wherein at least one of: (i) atleast one of an inlet path and an outlet path of the air separationchamber is disposed at least substantially vertically when the airseparation chamber is placed in an operating position; and (ii) at leastone of the inlet path to and the outlet path from the air separationchamber is disposed at least substantially at a same angle as the firstbaffle portion and the second baffle portion, respectively, of the airseparation chamber.